Just in case anyone else needs to replace their Pre3 glass/screen assembly, I can confirm that, assuming you've got a spare unit, the job can be done with a little care in about an hour or so.
Some things you'll want to note:
1. There are 7 + 2 Torx screws in total to release (size 4 or 5 - I used a size 5 driver successfully, but it felt like a size 4 would have been optimal.)
2. There is also an eighth screw on the inner panel - next to the camera lamp - no need to remove this one at all.
3. The first of the 7 screws needed to release the inner back-panel from the main circuit board are pretty obvious. See the very helpful photos by Rod Whitby (referenced above by DocJones).
4. The next '+1' is masked by a small label and recessed below the camera. Just press firmly with your driver to engage with the screw underneath. You can now remove the inner backpanel with no difficulty.
5. One final screw can be accessed once the inner panel is removed (right next to the volume switch assembly - see later). This will release the circuit-board from the screen-assembly - but read Step 6+ first!
6. *** Important *** The volume switch assembly (which also includes the headphone jack sub-circuit) is lightly glued to the screen-assembly BUT is otherwise attached to the circuit board and should remain so!
7. So, after removing the 7 +2 Torx screws, gently lift the glued sub-circuit from the metal screen-assembly before then lifting the circuit-board from the screen-assembly, with a little flexing of the catches around the back of the keyboard.
8. Then there is the main (long/thin) connector between screen-assembly and circuit-board - go easy lifting at either end to release it.
When replacing your circuit-board on to a fresh screen-assembly, take care to line-up the mounting posts with the holes in the board, while flexing it in to the catches around the back of the keyboard.
My spare screen-assembly actually came from a pre-production Pre3 and the alignment was not perfect. In my case, I needed to delicately 'extend' the mounting holes in the circuit-board to allow it to fit flush against the screen-assembly.